Method and device for reducing the acidic pollutant emissions of industrial installations

ABSTRACT

The invention relates to a method for reducing the acidic pollutant emissions, in particular the sulfur trioxide emission, of industrial installations with at least one burner for the combustion of liquid fossil fuels. In particular, the invention relates to flue gas neutralization in the combustion of heavy oils. According to the invention, it is proposed that, before the combustion, an emulsion of the fuel with a solution of a magnesium-containing active ingredient or a magnesium compound is formed, and led into the burner.

DESCRIPTION

[0001] The invention relates to a method for reducing the acidic pollutant emissions, particularly the sulfur trioxide emissions, of industrial installations with at least one burner for burning liquid fossil fuels. In particular, the invention relates to flue gas neutralization in the burning of heavy oils.

[0002] Flue gas neutralization in the burning of fossil fuels has been carried out for a long time to reduce the SO₃ content in the flue gas. A minimization of the SO₃ content decreases the tendency to soiling and the corrosion in the high and low temperature region of the boiler. In addition, the emission of rust flakes is avoided, and the surfaces of the boiler, which remain clear and which are clean, allow a more effective heat transfer.

[0003] It is known to add a neutralizing additive in the form of magnesium oxide powder to the fuel. Here the reactivity of the magnesium oxide depends essentially on the particle size of the added powder. However, there are limits to the SO₃ reduction in this process. The limits have a value of approximately 30%.

[0004] From EP 0 426 978 A1 it is known to add magnesium containing active ingredients in the form of a solution which is miscible with the liquid fuel. It is also known to add metallic soaps to the fuel. By these measures, the SO₃ reduction can be clearly improved to approximately 60%.

[0005] Furthermore, in principle, it is known to reduce the pollutant emissions not only by additives, which are added to the liquid fuel, but also by additives which are added to the flue gas. In the above mentioned patent, EP 0 426 976 A1, a method is disclosed in which a urea-containing and ammonia releasing reduction agent is led into the flue gases for reducing the content of oxides of nitrogen. From DE 44 17 874 C2 it is known to introduce, through a nozzle, an aqueous solution of a magnesium compound together with a NO_(x) reduction agent into the furnace. The purpose of this approach is to prevent the formation of ammonium hydrogen sulfates.

[0006] Using oil soluble additives has the drawback that they usually are combustible fluids. The fact that these additives are in part toxic substances represents a drawback. However, in particular, a drawback consists in that the entire magnesium containing compound introduced cannot be reacted because a part of the magnesium reacts with the fuel ash to form mixed oxides.

[0007] The invention is based on the problem of designing a method and a device of the type described above in such a manner that, for one thing, the handling of the additives used can be simplified. For another thing, an improved reaction is to be achieved with a view to recycling the introduced active ingredient.

[0008] According to the invention, the problem is solved by forming, prior to the combustion, an emulsion of the fuel with a solution of a magnesium-containing active ingredient or a magnesium compound, which is then introduced into the burner. This emulsion with the fuel can be formed, for example, with an aqueous solution of a water soluble magnesium containing active ingredient or a magnesium compound. As a result of this measure, the active ingredient, namely the magnesium compound, is finely distributed in its own liquid phase. The emulsion is finely divided in the fuel nozzle with a result that almost the entire quantity of magnesium-containing compound introduced can be reacted. No reaction with fuel ash occurs.

[0009] An additional advantage in using such a solution, and in particular, an aqueous solution of a water soluble magnesium containing active ingredient, consists in that the latter is not combustible. Therefore, the possibility exists of conveying the solution, which is added to the fuel, over relatively large distances within the industrial installation. Moreover, these solutions usually are not toxic so that there is no risk of environmental problems should a leak occur.

[0010] It is advantageous to introduce the solution into the fuel at high pressure. The use of high pressure promotes the formation of the emulsion in the fuel.

[0011] According to another embodiment variant of the invention, this solution of a magnesium-containing active ingredient or a magnesium compound is led into the combustion gases in the form of an aerosol. Here too, the solution can be an aqueous solution of water soluble magnesium compound. It is preferred to generate the aerosol with pressurized air, which is led into the solution to be introduced before the passage through a nozzle.

[0012] In the case of an aerosol as well, the magnesium-containing active ingredient or the magnesium compound is in its own liquid phase. Here too, a fine distribution of the liquid phase is effected so that almost all the magnesium-containing compound, for example MgSO₄, can react.

[0013] It is advantageous if the aerosol is introduced into the combustion gases at several places along the circumference of the combustion pipe, the flue gas pipe or the boiler passage with the formation of an umbrella of aerosol, which covers at least nearly completely the entire cross section. This has the advantage that the entire flue gas cross section is reached by the active ingredient. The leakage of unneutralized flue gases can thus be prevented or at least considerably reduced.

[0014] The magnesium-containing active ingredient, or the magnesium compound, can be, or contain, the salt of an organic or inorganic acid. One can also provide for the magnesium-containing active ingredient or the magnesium compound to contain magnesium nitrate and/or magnesium acetate.

[0015] Based on the preferred use of an aqueous solution of the water soluble magnesium compound, this additive which is added by metering can be conveyed without problem over longer distances within industrial installations. Here the advantage of the invention becomes particularly clear. One can use, in industrial installations which comprise a multitude of burners for burning liquid fossil fuels, a metering device and an introduction device which are associated with each burner, where the introduction device opens into the fuel line and, from a central delivery container, it leads this solution of the magnesium compound into the liquid with the formation of an emulsion with the fuel. The use of a central delivery container has the advantage that the handling and the use, as well as the refilling, of the solution by personnel can be considerably facilitated. One need only ensure that the central delivery container is always sufficiently filled with the solution in question.

[0016] It is advantageous if the introduction device opens into the fuel line in the flow direction of the fuel downstream from the fuel reconduction of each burner. This has the advantage that an undesired increase in the concentration of the solution in the fuel is prevented.

[0017] Furthermore, one can provide for the feed device to open into the fuel line in the flow direction of the fuel a small distance upstream from the burner nozzle. As a result, it is possible to prevent the re-agglomeration of the liquid phase of the active ingredient which is present in the emulsion, to form larger liquid drops. In principle, the added solution can also contain emulsifiers. Fine distribution in the atomization of the emulsion in the burner nozzle and a clean flame pattern are thus maintained.

[0018] It is advantageous to lead the solution under pressure to the individual burners, where each metering device comprises an adjustment valve.

[0019] This too considerably facilitates the handling, because only one pump is needed, which generates the required introduction pressure. Adjustment values can be regulated in a simple manner and controlled so that the required quantity of solution can be led to each burner depending on its individual consumption.

[0020] The invention is explained in greater detail below with reference to the diagrammatic drawings:

[0021]FIG. 1 shows a diagram of central additive feed in an industrial installation with several burners;

[0022]FIG. 2 shows the diagram of an additive introduction in an industrial installation with several combustion pipes into which the additive is fed; and

[0023]FIG. 3 shows a cross section through a combustion pipe with a multitude of nozzles for the introduction of the aerosol.

[0024]FIG. 1 shows a system for the introduction, into the fuel, of an additive for reducing the acid pollutant emission of industrial installations. There is a first delivery container 1 with a concentrate of the magnesium containing active ingredient or the magnesium compound. This magnesium-containing active ingredient can be, for example, a 20-60% magnesium acetate or magnesium nitrate solution. It is considered to be advantageous to use a dilution with water from 1:2 to 1:50, and in particular from 1:5 to 1:15. A second delivery container 2 is provided, which contains the carrier water for the formation of an aqueous solution in the desired final concentration of the solution to be introduced. In principle, this second delivery container 2 can be replaced by a central water supply.

[0025] The desired quantity of the concentrate from the delivery container 1 and the desired quantity of the carrier water from the delivery container 2 are led through a measurement device 3 and pumps 4 into a delivery container 5. The delivery container 5 thus contains the solution in the desired concentration, which is then led to the burners. The delivery container 5 is connected with a main distribution 6, which in turn is connected to a multitude of sub-distributions 7. Each sub-distribution 7 is connected with one or more feed devices 8, which open(s) into the fuel line 9 of a burner which is not shown. The details of the arrangement are such that the feed device 8 opens in the flow direction of the fuel, upstream from the fuel nozzle and downstream from the fuel reconduction into the fuel line 9. The feed device 8 also comprises an adjustment valve 10, by means of which the desired quantity of the aqueous solution is led into the fuel with the formation of an emulsion.

[0026] Because the use of an aqueous solution of a water soluble magnesium-containing active ingredient or a water soluble magnesium compound makes it possible to convey within the industrial installation over longer distances without problems, the addition of the given quantity at the desired concentration can be carried out by means of a simple valve control before each burner. In particular, it is not necessary to provide each burner with its own additive preparation installation with separate pump and separate metering device. Rather, the solution which is led into the fuel can be generated centrally, and mixed, and then it can be led through a corresponding distribution device 6, 7 and corresponding feed devices with metering devices 8, 10 into the fuel. As a result, the control of the introduced additive and the operation of the entire industrial installation are considerably simplified with the use of neutralizing additives.

[0027]FIG. 2 represents the feed of additive into the flue gas in an industrial installation with a multitude of combustion installations to be supplied. As far as the principle of the design is concerned, this additive feeding corresponds to the additive feeding into the fuel, and the same components, or components having the same effect, are denoted with the same reference numerals.

[0028] From the supply container 5, the ready-mixed additive reaches a main distribution 6, which is connected with a multitude of sub-distributions 7. A sub-distribution 7 is connected with a multitude of nozzles 11, through which the additive reaches the combustion gas. The nozzles can be present in the combustion pipe and/or in the flue gas duct and/or in the boiler pass of the combustion installation. For example, one can provide for each sub-distribution 7 to be allocated to a number of nozzles 11 which are arranged in a combustion pipe. However, it is also possible for one sub-distribution 7 to supply additive to nozzles in several combustion pipes.

[0029] The additive is led in the form of an aerosol into the combustion gases in the combustion pipe. For this purpose, the nozzles 11 are provided with a pressurized air inlet 12 to generate the aerosol. The pressurized air can be added to the additive at a pressure of 3.0-10.0 and, in particular, 5.0-7.0 bar. As a result, the aerosol can successively be injected over some distance through a nozzle into the combustion pipe.

[0030]FIG. 3 shows a possible arrangement of the nozzles for the introduction of the aerosol into the combustion pipe. The nozzles 11 are distributed essentially uniformly along the circumference and they are directed toward the middle of the combustion pipe. In principle, any other orientation of the nozzle is advantageous, provided that an essentially complete umbrella of aerosol covers the cross section. Overall, it is thus possible to achieve an effective neutralization of the combustion gases.

[0031]FIG. 1 shows the introduction of an additive into the fuel. FIGS. 2 and 3 show the introduction of an additive into the flue gas. Both additives have the same active ingredient, mainly a magnesium containing compound, which is preferably led in the form of an aqueous solution into the fuel or into the combustion gases. With reference to the quantity of fuel, one can carry out an addition of, for example, 5-500 mg MgO per 1 kg fuel. The introduced quantity, in both methods, is calculated depending on the specific properties of the fuel and the sulfur trioxide content in the waste gas. Here too, the formation of an emulsion on the one hand, and of an aerosol on the other, result in the active ingredient being present in its own liquid phase, which has an advantageous effect on the reactivity of the active ingredient and its complete reaction.

[0032] Naturally, it is also possible to use both methods in combination. For this purpose, one can provide, for example, downstream form the main distribution 6, a sub-distribution 7 for feeding aerosol nozzles 11, while another sub-distribution 7 supplies the feed device 10 for metering into the fuel. Even if the individual introduction devices or nozzles operate at a different pressure, said pressure can be generated by a corresponding number and a corresponding arrangement of throttle valves, or by additional pumps. 

1. Method for reducing the acidic pollutant emissions, particularly the sulfur trioxide emission, of industrial installations with at least one burner for burning liquid fossil fuels, characterized in that, before the combustion, an emulsion of the fuel is formed with a solution of a magnesium-containing active ingredient or a magnesium compound, and led into the burner.
 2. Method for reducing the acidic pollutant emissions, in particular the sulfur trioxide emission, of industrial installations with at least one burner for burning liquid fossil fuels, characterized in that, before the combustion, an aqueous solution of a water soluble magnesium-containing active ingredient or a magnesium compound is introduced into the fuel.
 3. Method according to claim 1, characterized in that the solution is introduced into the fuel at high pressure.
 4. Method for reducing the acidic pollutant emissions, in particular the sulfur trioxide emission, of industrial installations with at least one burner for burning liquid fossil fuels, characterized in that, an aerosol of an aqueous solution of a water soluble magnesium compound is introduced into the combustion gases.
 5. Method according to claim 4, characterized in that the aerosol is introduced into the combustion gases at several places along the circumference of the combustion pipe, with the formation of an umbrella of the aerosol, which covers the cross section at least approximately completely.
 6. Method according to one of claims 1-5, characterized in that the magnesium-containing active ingredient or the magnesium compound is, or contains, a salt of an organic or inorganic acid.
 7. Method according to one of claims 1-6, characterized in that the magnesium containing active ingredient or the magnesium compound contains magnesium nitrate and/or magnesium acetate.
 8. Device for reducing the acidic pollutant emissions, particularly the sulfur trioxide emission, of industrial installations, with one or a multitude of burners for burning liquid fossil fuels, characterized in that at least one, and preferably each, burner is associated with a metering device (10) and a feed device (8), which opens into the fuel line (9) and which leads, into the liquid fuel, a solution of a magnesium compound from a central supply container (5) with formation of an emulsion with the fuel.
 9. Device according to claim 8, characterized in that the introduction device opens into the fuel line in the flow direction of the fuel downstream from the fuel reconduction.
 10. Device according to one of claims 8 or 9, characterized in that the feed device opens into the fuel line in the flow direction of the fuel a short distance upstream from the burner nozzle.
 11. Device according to one of claims 8-10, characterized in that the solution is led under pressure into each burner, and in that each metering device comprises an adjustment valve (10).
 12. Device for the reduction of the acidic pollutant emissions, in particular the sulfur trioxide emission, of industrial installations, with one or a multitude of burners for burning liquid fossil fuels, characterized in that in at least one, and preferably in each combustion pipe and/or flue gas duct and/or boiler passage, at least one nozzle (11) with pressurized air inlet (12) is arranged, which nozzles are supplied from a central delivery container (5) with a solution of a magnesium compound, which solution is introduced into the combustion gases through a nozzle with pressurized air and with the formation of an aerosol. 